Information retrieval in the form of discs having information distributed in a circular or spiral pattern has been available in various forms for many years. Early forms of musical reproduction equipment, for example, used discs with either holes or protuberances to pluck an array of strings or vibrating posts to produce music. Early displays of moving pictures operated by rotation of a disc bearing consecutive images on the periphery. The most common form of storing reproductions of musical performances, which has been in use for about one hundred years, is the phonograph record which uses a spiral pattern of grooves having vertical and horizontal modulations to generate signals which can be converted to sound.
With the introduction of the laser to industry, a new information storage system was developed which comprised a disc having a circular or spiral pattern of depressions or protuberances which would disturb, reflect, or refract incident light patterns. These information storing discs, often used for storage of audio/visual information and generally referred to as video discs, are well known in the art. Such U.S. Pat. Nos. as 3,658,954 (Apr. 25, 1972); 3,795,534 (Mar. 5, 1974); 3,798,134 (Mar. 19, 1974); 3,855,426 (Dec. 17, 1974); 3,901,994 (Aug. 26, 1975); 4,124,672 (Nov. 7, 1978); 4,126,726 (Nov. 21, 1978); and 4,130,620 (Dec. 19, 1978) show various constructions, compositions, and processes for forming video discs.
In addition to the laser readable video disc, another commericial construction is used which is more similar to the classic phonograph recording. This type of construction, as described in RCA Review, Vol. 39, No. 1, March 1978, comprises a spiral array of grooves which is tracked by a stylus. The grooves are impressed with coded information in the form of vertical and/or radial modulations.
Even though these systems are read by totally different techniques, they are affected by similar, if not identical, problems. Imperfections in the depressions, protuberances, or modulations cause undesirable or spurious signals to be generated. The imperfections can be produced during manufacture of the disc or can develop from wear during use or manipulation of the disc.
The present invention relates to information storage discs for use with laser or stylus readout systems which have good fidelity and resistance to wear.